how to fix P0301 misfire code in BMW 3 Series E90/E91 (2005-2012)

Solution

1. Preparation

• Gather tools and parts before starting the repair.
• Disconnect the negative battery terminal to prevent electrical shock.
• Allow the engine to cool down completely.

2. Replace Spark Plug

• Tools Required: Spark plug socket, ratchet, torque wrench, dielectric grease.
• Remove the engine cover if applicable.
• Disconnect the ignition coil connector for cylinder 1.
• Remove the ignition coil by unscrewing the retaining bolt and gently pulling it out.
• Remove the spark plug using the spark plug socket.
• Inspect the old spark plug; if it shows signs of damage, replace it with a new one.
• Apply a small amount of dielectric grease to the new spark plug’s threads.
• Install the new spark plug and torque it to the manufacturer’s specification (typically around 18-22 ft-lbs).
• Reinstall the ignition coil and secure it in place.
• Reconnect the ignition coil connector.

3. Replace Ignition Coil (if necessary)

• If the ignition coil was found faulty during diagnostics, replace it.
• Tools Required: Same as above.
• Remove the faulty ignition coil as described in the previous step.
• Install the new ignition coil and ensure it is seated properly.
• Reconnect the coil connector.

4. Clean or Replace Fuel Injector (if necessary)

• If the fuel injector was assessed to be clogged or malfunctioning, remove and clean or replace it.
• Tools Required: Injector removal tool, fuel line tool, cleaning solvent or new injector.
• Relieve fuel pressure from the system before disconnecting fuel lines.
• Disconnect the fuel line and electrical connector from the injector.
• Remove the injector from the rail.
• Clean the injector with an appropriate cleaning solution or replace it with a new injector.
• Reinstall the injector and reconnect fuel lines and electrical connectors.

5. Reassemble and Inspect

• Reassemble any components removed during the repair.
• Reconnect the negative battery terminal.
• Start the engine and check for smooth operation.